A week of field-research in tsunami-ravaged Sri Lanka conducted by a delegation of scientists lead by Prof. Philip Lui, civil and environmental engineering, was completed last Saturday and presented in a seminar at the Bandaranaike Memorial International Conference Hall in Colombo, Sri Lanka.
The delegation, comprised of Lui and several scientists from universities around the country and the U.S. Geological Survey (USGS), spent most of their time searching coastal regions for scientific evidence that would shed light on the physics and geological impacts of the tsunami.
“We covered a large region, close to about 300 km,” said Prof. Harindra Fernando, mechanical engineering at Arizona State University, and part of the delegation. This was accomplished by two simultaneous expeditions: one led by Fernando and the other led by Lui. Scientists from each group spoke with eyewitnesses, studied sediment deposits, surveyed local damage, and looked for other evidence including “water marks, [and] debris marks,” Fernando explained.
From the collected evidence, the expeditions’ scientists were able to conclude the height of the tsunami as it arrived on shore and the extent of the wave’s flooding. “We found tsunami elevations that were 4 meters in most places and inundations approaching 4 km,” said Prof. Patrick Lynett ’92, civil engineering, Texas A&M.
The extensive damage also shed light on the intensity of the tsunami, though much of it was also a result of low building standards, according to Lynett. In the first two rows adjacent to the ocean, “most of the buildings were completely destroyed … knocked down to their foundation,” Lynett said.
The layers of sand that were deposited by the tsunami provided the expeditions’ geologists with a lot of information about the tsunami. For example, after some analysis in a lab, the sand deposits will “tell [us] how fast the tsunami was moving,” said Bruce Jaffe of USGS. Also, since the depth of the tsunami is related to its speed, the sand deposits will indirectly act as good “indicators of how deep the flow was,” Jaffe added.
In most cases, however, the characteristics of the tsunami were not uniform across the affected coast line. The inlets, headlands, and other geographical intricacies of the coastal regions made the behavior of the tsunami as it hit shore very location specific. The impacts “depended on the microscale features of the coast line,” explained Fernando, and the coast line is characterized by “a lot of heterogeneity in the landscape.”
The central purpose of the field research, however, was to collect information that might improve the predictability of tsunamis, according to Lui. Currently, “tsunamis are not at all predictable,” Fernando said, because the mechanisms that trigger them, usually under-water land slides or earthquakes, are not predictable. However, once a tsunami has been generated in the ocean, its evolution can be determined with the aid of physical models, according to Lynett.
With the tsunami that affected Sri Lanka, the models did quite well in predicting the wave heights and the extent of the flooding. “The model predictions were in the ball park of 3 to 6 meters,” Lynett said. “They were quite reasonable,” he added.
However, these physical models require initial conditions in order to describe the evolution of the tsunami. “You need to know some information about the characteristics of the earthquake,” Lynett said. This information is available in some parts of the world from deep ocean buoys, which have been deployed in some parts of the Pacific Ocean by the National Oceanic and Atmospheric Administration, but not in the Indian Ocean where this last tsunami occurred. In addition to deep sea buoys, “you need a warning center, [and] people that can work with the data,” Lynett explained. A NOAA administrated tsunami prediction center exists in Hawaii.
After Saturday’s seminar in Sri Lanka, Lui was asked to travel to Thailand to survey to effects of the tsunami there.
Though, just how much the expedition’s findings will aid in improving tsunami predictability is not yet known, the field-research has clearly “improve[ed] the record of past tsunamis,” Jaffe said.
Archived article by David Andrade
Sun Staff Writer